Computing devices such as personal computers (PCs) typically include one or more printed circuit boards (PCBs) on which various components are mounted. Traditionally, such components are mounted to PCBs using surface mount technology in which the components are secured to the PCB using solder paste. More recently, press-fit technology has been developed through which pins, either those of a given component or individually, are pressed into a PCB using a large force, such as several tons.
FIGS. 1A and 1B illustrate an example of press fitting of individual connector pins 100 into a PCB 102. As is depicted in those figures, the pins 100 are passed through holes 104, called through holes, that extend from a bottom side 106 of the PCB 102 to a top side 108 of the PCB. The through holes 104 often comprise metal barrels 110 that extend along the length of the holes. The pins 100 are held in place within the barrels 110 by deformable portions of the pins (not shown) that are inwardly compressed when the pins are pressed into the PCB 102 from the bottom side of the PCB using base portions 112 of the pins.
It is common to inspect the connection of components to a PCB during manufacturing to ensure that the various components are correctly mounted to the PCB. One common inspection method is two-dimensional automatic optical inspection (AOI) in which machine vision techniques are used to analyze the connection of the components to the PCB. Although two-dimensional AOI is reasonably effective for inspecting the connection of components that have been attached to the PCB using surface mount technology, AOI is less effective for inspecting press-fit connections. The reason for this is that, for a proper connection, a pin must protrude a given distance beyond the top surface of the PCB (see FIGS. 1A and 1B). AOI techniques, however, only employ two-dimensional viewing from a position directly above the PCB. Therefore, AOI cannot distinguish between a pin that correctly protrudes from its through hole, and a pin that is wholly contained within the through hole (e.g., due to crimping or folding of the pin within the through hole). Moreover, it is possible for AOI techniques to falsely indicate a proper press-fit connection even when a pin is not contained within a through hole by mistakenly identifying the through hole barrel as a pin.
Although proper mounting of a press-fit connector pin could be confirmed using three-dimensional inspection equipment (e.g., three-dimensional AOI), such equipment is undesirably complex. For example, to properly inspect a pin in three dimensions, such equipment may require as many as five cameras, one camera positioned directly above the pin and four cameras placed at various lateral positions around the perimeter of the pin. In addition to the expense of such equipment, complex software must be used to coordinate and analyze all of the data collected by the three-dimensional inspection equipment.
From the above, it can be appreciated that it would be desirable to have a system and method for effectively inspecting press-fit connections that does not require three-dimensional inspection equipment.